The Port of Grays Harbor in Washington is a bustling center of shipping on the West Coast of the U.S. Only two hours from the deep waters of the Pacific, the 1,400-foot-long (430-meter [m]) Terminal 4 is capable of handling heavy industrial equipment and other large cargo such as automotive imports and exports. Water depths of about 40 feet (12 m), on-dock railroad access to BNSF and Union Pacific lines, and covered warehouse spaces, among other features, make the port attractive to shippers from as far away as Asia and Africa.
Because it sits along the Chehalis River, Terminal 4 is prone to an age-old problem: sediment of up to 20 feet a year accumulates as the river enters the protected bay. For decades, dredging kept the waterway clear for the large ships that call on the port. By the 1970s and early 1980s, dredging the channel using diesel-driven mechanical equipment was costing the port between $1 million and $2 million a year, an operating cost the port found difficult to sustain.
When the port expanded Terminal 4 in the 1980s, commissioners decided to install a permanent jet array pumping system to remove sediment, maintain proper depths, and save energy and costs. Sediment removal is accomplished with water jets driven by twin 400-horsepower (hp) electric pumps that are operated in a timed sequence during the twice-daily ebb tide. Part of the jet array system was a 30-hp air compressor that was used to actuate the pneumatic valves required to sync the water distribution network.
While the jet array pumping system allowed the port to self-scour the sediment away to give vessels access to Terminal 4’s north and south berth, it carried costs of its own. By 2010, the power bill from the local utility, Grays Harbor Public Utility District, served by the federal Bonneville Power Administration (BPA), was about $230,000 a year.
So in 2011, the Port of Grays Harbor called in engineers from the Washington State University (WSU) Energy Program to see if the 400-hp pumps in the jet array system were becoming inefficient as they aged.
The engineers took flow, pressure and power readings using energy loggers. They found that the pumps were operating within their specified pump curves. A separate study of nozzle-firing sequences was unable to determine whether reducing the time would result in satisfactory sediment clearance.
“We told them the pumps were as efficient as the day they were made, but that the overall system might still be wasting energy,” said Tony Simon, a WSU Energy Program engineer who worked on the project. “My colleague, Gil McCoy, asked if there was any way to monitor the underwater sediment removal in real time to determine how effectively the pumps were really doing their job.”
The team members then began a search to find out how they might use technology to monitor the seafloor to measure the buildup of sediment and the effectiveness of the jet array system.
They connected with a sonar technology company.
“The company is a spin off of the University of Washington Applied Physics Laboratory,” Simon said. “They helped us by performing some sonar tests at the port and said, ‘Yeah, we can definitely see everything underneath there. It’s a good opportunity.’”
So the group got approval from the port and, by 2012, the WSU Energy Program engineers had also worked with the local utility and BPA’s Energy Smart Industrial Program to secure a grant to research the issue. They first deployed 3-D multi-beam scanning sonar technology to provide imagery of the underwater landscape with accurate measurement capabilities to ensure a minimum depth of 40 feet was maintained.
With accurate measurements of what was going on below the surface, they could turn their attention to achieving sediment-removal goals while reducing the pump system operating time. The port purchased an energy management system to keep tabs on the pumps over time. Using an energy logger, the WSU Energy Program engineers established a correlation between electrical current and kilowatts, which helped the port.
“When we’re talking energy, these induction motors, like the ones on these pumps and a lot of other equipment, use a fraction of the current to energize the machine, which doesn’t register on the utility meter,” Simon said. “And even though current is making the meter spin, not all the current equals energy. That’s why taking a measurement with a true power meter comes into play. Meters like that use voltage and current measurements to determine the power factor and, ultimately, the kilowatts. It’s very important to have this information to know what the motor load is and what equates to actual kilowatts.”
In many motor-driven systems, motor loads can vary, which affects the power factor, kilowatts and current draw. At the port, the team conducted data logging over an extended period of time to determine the pumping system’s operating characteristics. Because an energy management system was going to be evaluated, the engineers needed to be certain that they fully understood the system’s baseline operation. The energy management system was only measuring current, so the engineers used a power measurement from the meter to derive a multiplier that they used in the unit’s software to convert current to kilowatts (kW) and kilowatt-hours (kWh), the measurement used to calculate utility charges.